MapSource is a free application developed by Garmin to help its users upload map data, points of interest, waypoints and routes to their Garmin GPS units. All Garmin devices come with MapSource. However, if you purchased a second-hand GPS unit, you might not have the CD that contains MapSource. Unfortunately, you can download only a MapSource version update from Garmin. If you didn't install Garmin from the CD that came with the GPS unit, the installer will not install the software because it can't find the previous version. However, there is a workaround this issue.